Size-dependent Cannibalism Research Articles

Optimal reproductive phenology under size-dependent cannibalism.

Intra‐cohort cannibalism is an example of a size‐mediated priority effect. If early life stages cannibalize slightly smaller individuals, then parents face a trade‐off between breeding at the best time for larval growth or development and predation risk from offspring born earlier. This game‐theoretic situation among parents may drive adaptive reproductive phenology toward earlier breeding. However, it is not straightforward to quantify how cannibalism affects seasonal egg fitness or to distinguish emergent breeding phenology from alternative adaptive drivers. Here, we devise an age‐structured game‐theoretic mathematical model to find evolutionary stable breeding phenologies. We predict how size‐dependent cannibalism acting on eggs, larvae, or both changes emergent breeding phenology and find that breeding under inter‐cohort cannibalism occurs earlier than the optimal match to environmental conditions. We show that emergent breeding phenology patterns at the level of the population are sensitive to the ontogeny of cannibalism, that is, which life stage is subject to cannibalism. This suggests that the nature of cannibalism among early life stages is a potential driver of the diversity of reproductive phenologies seen across taxa and may be a contributing factor in situations where breeding occurs earlier than expected from environmental conditions.

Effects of resource-dependent cannibalism on population size distribution and individual life history in a case-bearing caddisfly.

Resource availability often determines the intensity of cannibalism, which has a considerable effect on population size distribution and individual life history. Larvae of the caddisfly Psilotreta kisoensis build portable cases from sedimentary sands and often display cannibalism. For this species, the availability of preferable case material is a critical factor that affects larval fitness, and material is locally variable depending on the underlying geology. In this study, we investigated how sand quality as a case material determines cannibalism frequency among larvae and, in turn, how the differential cannibalism frequency affects the body-size distribution and voltinism. Rearing experiments within a cohort revealed that a bimodal size distribution developed regardless of material quality. However, as the preferable material became abundant, the proportion of larger to smaller individuals increased. Consecutive experiments suggested that smaller larvae were more frequently cannibalized by larger ones and excluded from the population when preferable smooth material was abundant. This frequent cannibalism resulted in a bimodal size distribution with a significantly higher proportion of larger compared to smaller individuals. The size-dependent cannibalism was significantly suppressed when the larvae were raised in an environment with a scarcity of the preferable case material. This is probably because larvae cannot enjoy the benefit of rapid growth by cannibalism due to the difficulties in enlarging their case. At low cannibalism the growth of smaller individuals was stunted, and this was probably due to risk of cannibalism by larger individuals. This growth reduction in small individuals led to a bimodal size-distribution but with a lower proportion of larger to smaller individuals compared to at high cannibalism. A field study in two streams showed a similar size distribution of larvae as was found in the rearing experiment. The bimodal ratio has consequences for life history, since a size-bimodal population causes a cohort splitting: only larvae that were fully grown at 1 year had a univoltine life cycle, whereas larvae with a stunted growth continued their larval life for another year (semivoltine). This study suggests that availability of preferable case building material is an important factor that affects cannibalism, which in turn affects larval population size structure and cohort splitting.

Modelling Size-Dependent Cannibalism in Barramundi Lates calcarifer: Cannibalistic Polyphenism and Its Implication to Aquaculture

This study quantified size-dependent cannibalism in barramundi Lates calcarifer through coupling a range of prey-predator pairs in a different range of fish sizes. Predictive models were developed using morphological traits with the alterative assumption of cannibalistic polyphenism. Predictive models were validated with the data from trials where cannibals were challenged with progressing increments of prey sizes. The experimental observations showed that cannibals of 25–131 mm total length could ingest the conspecific prey of 78–72% cannibal length. In the validation test, all predictive models underestimate the maximum ingestible prey size for cannibals of a similar size range. However, the model based on the maximal mouth width at opening closely matched the empirical observations, suggesting a certain degree of phenotypic plasticity of mouth size among cannibalistic individuals. Mouth size showed allometric growth comparing with body depth, resulting in a decreasing trend on the maximum size of ingestible prey as cannibals grow larger, which in parts explains why cannibalism in barramundi is frequently observed in the early developmental stage. Any barramundi has the potential to become a cannibal when the initial prey size was <50% of the cannibal body length, but fish could never become a cannibal when prey were >58% of their size, suggesting that 50% of size difference can be the threshold to initiate intracohort cannibalism in a barramundi population. Cannibalistic polyphenism was likely to occur in barramundi that had a cannibalistic history. An experienced cannibal would have a greater ability to stretch its mouth size to capture a much larger prey than the models predict. The awareness of cannibalistic polyphenism has important application in fish farming management to reduce cannibalism.

Are cannibalism and tarantula predation factors in the spatial distribution of the wolf spider Lycosa subfusca (Araneae Lycosidae)?

In this work we studied the effect of size-dependent predation and cannibalism on the spatial distribution of the wolf spider Lycosa subfusca, which shares its habitat with a bigger spider: the tarantula Brachypelma vagans, in the Yucatan Peninsula. We examined (i) in the field, the predation interaction between medium tarantulas and large, medium and small wolf spiders; (ii) in the laboratory, size-dependent cannibalism in the wolf spider; and (iii) the simultaneous occurrence of small, medium and large tarantulas, and small, medium and large wolf spiders in three sites in the field (secondary forest, backyard and grazed lawn). In predation interactions, tarantulas attacked large wolf spiders more frequently than medium ones (55% vs 25%), and never attacked small ones. Cannibalism experiments in the wolf spider showed that attack was always initiated by the larger individual. Attack frequencies increased with spider size, but capture success was similar regardless of spider size. Medium and large wolf spiders were much more abundant in the secondary forest, where tarantulas were absent, than in the other two sites. In contrast, small wolf spiders were much more abundant than large ones in both the backyard and grazed lawn, where tarantulas were common. Spatial segregation of large wolf spiders in the secondary forest appears to be related to the absence of tarantulas. On the other hand, small wolf spiders may prefer sites with tarantulas to avoid predation by larger wolf spiders. In conclusion, the spatial distribution of Lycosa subfusca seems to be the result of the predation by tarantulas and conspecifics.

What causes cannibalization-associated suffocation in cultured brown-marbled grouper,Epinephelus fuscoguttatus(Forsskål, 1775)?

During culture of grouper, cannibalism is a frequent phenomenon that usually causes economic loss. Grouper culture often requires grading to prevent size-dependent cannibalism. In comparison with orange-spotted (Epinephelus coioides) and giant grouper (E. lanceolatus), failure to swallow prey during cannibalism is frequently observed in brown-marbled grouper (E. fuscoguttatus). The cannibal cannot engulf the entire prey and the two fish ultimately end up dying together. Herein, we attempted to compare morphometric differences among orange-spotted, giant and brown-marbled grouper. We established a cannibal–prey total length (TL) relationship for brown-marbled grouper: TLprey=0.71 TLcannibal−1.75. According to the equation, a difference of approximately 50% in TL is a threshold to use for grading the grouper. This value is much larger than that used (30%) in orange-spotted and giant grouper, and this size difference results in a higher incidence of failed cannibalism attempts in brown-marbled grouper. It is our belief that the standard grading method will fail to produce as good an effect in brown-marbled grouper as is seen in orange-spotted and giant grouper. Therefore, in addition to grading, other manipulations such as satiation feeding, nutritional supplementation and optimal stocking densities should be applied to reduce cannibalism of brown-marbled grouper.

Prediction of cannibalism in juvenile Oreochromis niloticus based on predator to prey weight ratio, and effects of age and stocking density

Factors influencing size-dependent cannibalism in Nile tilapia, Oreochromis niloticus, were investigated in controlled conditions. First, individual-based trials were conducted to develop a linear regression model to predict the occurrence of cannibalism based on body measurements. Oral gape ( G, mm), body depth ( D, mm) and weight ( W, g) of 140 fish were measured and we estimated maximum prey weight ( W prey) for a given predator weight ( W predator): Log 10 W prey = 1.03Log 10 W predator − 1.13. This model was verified by conducting 76 single pair trials. The revised model based on observed cannibalism is: Log 10 W prey = Log 10 W predator − 1.17. Several experiments involving a group of prey and predators were conducted to elucidate the relative importance of factors that influence cannibalism. Cannibalism was significantly affected by stocking density, age of fish and predator/prey weight ratio. Logit models of mortality data of both the individual-based and observations based on a group of predators and prey estimated R 50 (the predator/prey weight ratio at which an encounter of a predator and prey resulted in a predation success of 50%) to be 14.6 and 14.8, respectively. The results of these experiments can be used to reduce fry losses due to cannibalism.

Parasitism increases offspring size in a damselfly: experimental evidence for parasite-mediated maternal effects

The effects of parasites on host fitness and the fitness effects of maternal effects are widely discussed. In this study, I conducted an experiment linking both aspects. I manipulated the ectoparasite load (Acari: Arrenurus cuspidator) of damselflies, Coenagrion puella, and found that larvae from mothers with high parasite loads were larger (assessed by head width) than larvae from mothers with low parasite loads. Furthermore, there was a negative correlation between the number of eggs laid and parasite load. Parasitized mothers thus seemed to have fewer, but probably better, offspring. The ecological significance of these parasite-mediated maternal effects remains to be tested. However, size-dependent cannibalism almost certainly has important consequences for population dynamics.

Size-Dependent Cannibalism in Praying Mantids: Using Biomass Flux to Model Size-Structured Populations

Here we investigate how cannibalism, a widespread phenomenon in nature, influences the population dynamics and the differential success of emergence-timing strategies in praying mantids. Relying on an extraordinarily complete data set describing the ecophysiology of a single mantid species, we construct a size-structured model based on "biomass flux" to study how size-dependent cannibalism influences this species' population ecology. Further, we demonstrate how this model accurately predicts mantid developmental patterns under both laboratory and field conditions. We conclude that for mantids, and perhaps generalist ambush predators overall, descriptions of biomass flux can be satisfactorily used to model growth without explicit reliance on encounter rate terms. In particular, this autecological approach to modeling size-structured interactions provides a method for revealing how sensitively development hinges on small differences in emergence time.